Excimer lasers are molecular lasers which have a metastable excited state. The lasing medium is a gas which usually consists of active components such as a halogen/rare gas combination in an inert buffer such helium or neon. Heretofore the buffer gas has usually been either pure neon or pure helium. This known choice of neon or helium gives the user the option between a high cost gas with high output power or a low cost gas with a lower laser power output. For example, the use of the relatively cheaper helium as the buffer gas typically yields only 60 to 70% of the power achieved with a pure neon buffer gas.
It is known from European Patent Publication No. 0430411 for a gas mixture for an excimer laser to contain about 99% of one or more of helium and neon. However, this document does not give details of the percentage of helium or neon in the inert buffer. U.S. Pat. No. 4674099 describes a typical lasing gas mixture including a diluent rare gas such as helium and/or neon in concentrations in the order of 95%. Again, this document does not give details of any helium/neon mixture.
For the avoidance of doubt the expression "buffer gas" used throughout this specification is intended to embrace the inert gas(es) which represent the balance of the lasing gas mixture excluding the active lasing constituents.
Laser gases are expensive and efforts are continuously being made to reduce costs in this area.